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Insane Question

I have a crazy question. Its crazy because nobody else on the planet would want to heat their pool anywhere near as much as my wife.

My pool is 18' by 38' IG Liner. I have a minimax 250 which is probably a little under powered for this size pool. But it does the job like a champ. Thing is well over 10 years old and doesn't give me any problems.

My Pool guy who is a magician retrofitted a digital thermostat onto it so now I have great control over the pool temp and spa temp. Before I just had to turn the dial up and hope for the best.

Anyway, here is the issue. My wife is insane. And she likes to swim at night a lot. But she won't swim unless the water is about 93 degrees.
The heater starts cutting on and off every 2 minutes or so when the pool gets to 90 degrees. It has a very difficult time climbing to 91... But turns on and off so often that it wont go any higher.

I would think this is a thermostat problem of the heater in which it was protecting itself or something, but if I turn on the spa, it easily can make the spa 104 degrees without cutting on and off. I know its obviously a lot easier to heat up a tiny spa than a big pool, but the temp of the water is the temp of the water, right? So if the heater will stay on all the way from 80 to 104 for the spa, why would it cut off at 90 for the pool itself? I would think there has to be some other issue going on...

This would not be any issue at all if my wife was normal. And I know it would be a lot cheaper if I just forced her to move to Arizona or Texas. But its odd to me and I was hoping someone here might know why this might happen.

Re: Insane Question

Where is the temp sensor located relative to the return that's injecting the warm water? Sounds like heat cycling to me maybe because the temp sensor is too close to the return and see's the temp rise to setpoint then cool back off.

Re: Insane Question

Originally Posted by Bama Rambler

Where is the temp sensor located relative to the return that's injecting the warm water? Sounds like heat cycling to me maybe because the temp sensor is too close to the return and see's the temp rise to setpoint then cool back off.

Thanks. The temp sensor I believe is before the heater. Its pretty close to the pump.
Also the temperature of the temp sensor seems accurate within about 2 degrees of my pool thermometer. So it will say 92 and my pool will be 90. But I have it set for 96 or higher.
Also if it was my temp sensor, wouldnt it not be working properly for the spa?

Re: Insane Question

Any chance that the hotter water from the return is getting to the skimmer and being pulled back to the pump where the sensor sees it and thinks the whole pool is warm enough? A couple of ideas to check that out: Shut off the skimmer and operate on drain only, or more drain than skimmer if that doesn't work. Another option would be to hook a vacuum to the skimmer and place the end of the hose on the bottom in the deep end. That way you'd be pulling the coolest water in the pool back to the pump. It could be as simple as re-aiming a return eyeball.

Re: Insane Question

Originally Posted by JohnT

Any chance that the hotter water from the return is getting to the skimmer and being pulled back to the pump where the sensor sees it and thinks the whole pool is warm enough? A couple of ideas to check that out: Shut off the skimmer and operate on drain only, or more drain than skimmer if that doesn't work. Another option would be to hook a vacuum to the skimmer and place the end of the hose on the bottom in the deep end. That way you'd be pulling the coolest water in the pool back to the pump. It could be as simple as re-aiming a return eyeball.

That seems extremely logical, but it can't be the sensor because there is a thermostat on it that tells me the temperature that the sensor is seeing. And it is much lower than what I have it set at. Plus, the device I have tells me if the heater should be on or off with a green light. The green light is consistantly on, meaning the heater should be on. Yet the heater is cycling on and off every minute... But the sensor isnt telling it to.

The weirdest part though is that if I switch everything to spa mode, and the water in the spa is currently 78 degrees, it will heat straight up to 105 without the heater turning off once. So I know it isnt a safety feature of the heaters to turn off on its own. The whole thing doesnt make sense. It runs perfect until 90 in the pool and then like clockwork starts cutting off...

Re: Insane Question

Originally Posted by mitch08

The weirdest part though is that if I switch everything to spa mode, and the water in the spa is currently 78 degrees, it will heat straight up to 105 without the heater turning off once. So I know it isnt a safety feature of the heaters to turn off on its own. The whole thing doesnt make sense. It runs perfect until 90 in the pool and then like clockwork starts cutting off...

In spa mode, does the heater pull water from the pool and return only to the spa, or does it pull a mixture from the spa and pool or from the spa only? I wonder if there is an internal heater temp limit on incoming water temperature to avoid sending out water that may be unsafe for bathers or equipment. That wouldn't be an issue if the heater draws in pool water in spa mode, but it could be an issue if you are heating the pool water higher than the threshold.

Re: Insane Question

I have a thought. The heaters has an internal overheat shutdown. Normally that won't get triggered till the output water reaches around 120. If the flow rate is enough lower in pool mode than it is in spa mode, the water will get hotter in the heater in pool mode than it does when in spa mode. That could be enough to trigger the overheat sensor, especially if it is triggering early.

One quick way to check into this possibility is to look at the filter pressure in pool mode and in spa mode. If the pressure is higher in pool mode, this is worth investigating. This could also happen if pool mode runs the pump on a lower speed than spa mode does.

Re: Insane Question

Sounds like you have a problem with the fancy digital electronic control board. The heater is using the same set of protection switches (thermolink, high limit, over limit, pressure switch, etc), regardless of if it's in pool mode or spa mode.

You should have a toggle switch or terminal positions on the display board that shows Pool - Common - Spa, and three wires to it. Switch the Pool wire with the spa wire and then run your system in SPA mode. See if the system still spits and sputters when it gets to 92 degrees. If so, your control board is not working properly in the pool mode.

I recommended testing in the spa mode because there's less water and it should be quicker to get a few hundred gallons up to temperature than many thousand gallons of your pool.

Re: Insane Question

Thank you very much everyone. I never expected so many people to help out. Everytime I post a question, I am honestly shocked by how incredible everyone here is!!!

Just to clarify a couple of things though. The heater is ancient. It has a switch that flips from off to pool to spa. But both the pool and spa are actually hooked up to pool. I only use the heater in one mode. So I turn the heater on by flipping the switch and then I adjust the temperature on the retrofitted digital thermostat.

Going from pool mode to spa mode is pretty typical of spill over spa setups. A couple of levers that controls the water flow. When I am in spa mode, the suction and return comes only from the spa. When in pool mode the suction and return comes only from the pool. When its spilling over the suction comes from the pool and returns through the spa. Pretty basic. the heater has no idea which is which. It is purely controlled by the settings on the thermostat.

Some of you guys have some great ideas and I am going to look into them and try your suggestions. But seriously thanks for taking the time to help out!

Launboy: I did have the exact same problem before the retrofit, but it was worse. The heater would cut off when the spa was about 99 degrees due to the internal thermostat of the heater. It was terrible which is one of the reasons I had my guy put the digital thermostat in. And for the most part it works excellent because I can control the spa temp perfectly.

Jasonlion: That is a definite possiblility. I am going to check out my pressure tomorrow. It would be funny if all I needed was a backwash to get the thing to stay on for a couple of extra degrees.

Re: Insane Question

LOL, when I was a kid I was able to swim in any water. I never even thought about it.
You just jumped in and 10 minutes later you warmed up

But now forget that!!! It could be 110 degrees out and I cant get in the pool unless it is 86 or higher. ROFL!!!
My wife needs it to be about 88 or she will complain. But that is during the day. At night when it is cooler out she wants the low to mid 90s. Plus she always goes in the spa first... And no matter how warm the pool is, when you are in a 103 degree spa and then jump into the pool, the initial feeling is really cold. You get used to it in about 3 seconds, but that entry is tough.

But 93 degrees IMO is extreme. Not only is it uncomfortably warm for a pool, but my gas bill is becoming stupid expensive.

Re: Insane Question

Originally Posted by mitch08

[But 93 degrees IMO is extreme. Not only is it uncomfortably warm for a pool, but my gas bill is becoming stupid expensive.

Maybe you should just tell her the problem is "unfixable"(even though you'll have fixed it) and the pool will never be above 90 because the short cycling will damage the heater. Just don't let her mess with the control and find out it works or

**Disclaimer, I will not be held responsible for any punishment enacted upon the OP if the above suggestion is tried and fails.**

Re: Insane Question

Kinda like floating in bathwater. It's very nice for night swimming.

On a hot day it's def too warm and not refreshing at all...86 is better on a hot day. I tend not to get in if it's less than 84 and only then if I HAVE to. I got in on a hot day at 78 and that was cause I HAD to vacume. It wasn't awful, but not for me.

Re: Insane Question

Originally Posted by frustratedpoolmom

Kinda like floating in bathwater. It's very nice for night swimming.

On a hot day it's def too warm and not refreshing at all...86 is better on a hot day. I tend not to get in if it's less than 84 and only then if I HAVE to. I got in on a hot day at 78 and that was cause I HAD to vacume. It wasn't awful, but not for me.

I agree with you 100%. When it is hot out I like it to be between 86 and 88.
But that is too cold for the nights in NY when the temp drops I like right around 90 at night.